Weed of the Month: Eastern Black Nightshade

Published: June 6, 2011

Eastern black nightshade (Solanum ptycanthum) is an erect summer annual with a distribution found primarily east of the Rocky Mountains, but in recent years has been found more commonly in Kentucky, Illinois, Indiana, and Missouri (Ogg and Rogers 1989; Young et al. 2002; Uva et al. 1997). Eastern black nightshade typically germinates from May through July in the Midwest (Myers et al. 2005; Zhou et al. 2005.)

Figure 1: Eastern Black Nightshade seedling

Eastern black nightshade seedlings have cotyledons that are green on the upper surface, and purple- or maroon-tinted on the lower surface. Stems below these cotyledons are covered with small hairs and are also green to sometimes tinted maroon (Figures 1 and 2). The leaves are simple, arranged alternately along the stem, ovate or ovate to lanceolate in outline, with leaf margins that may either be entire or with blunt teeth (Figure 3). Leaves are often only slightly hairy, but this characteristic can vary from plant to plant. Stems of eastern black nightshade are round and angular, partially hairy, and branching, with a purplish color, and can become woody as the plant matures. White or purple-tinged star-shaped flowers may be present from mid-June throughout summer with glossy black berries maturing 4 to 5 weeks after flowering. The clusters of berries that are produced are capable of producing hundreds of thousands of seed per growing season (Ward and Weaver 1996; Ogg and Rogers 1989).

Figure 2: Eastern Black Nightshade seedling

One of the most common and well known problems associated with eastern black nightshade is its toxicity to livestock. With the exception of the mature berries, the vegetative parts and fruit contain a chemical known as glycoalkaloid solanine which, when ingested, produces a gastrointestinal irritation in all classes of livestock (Uva et al. 1997). In row crop production, eastern black nightshade has become a more notable problem in recent years, especially in soybeans. Although this plant is capable of competing with the crop and reducing soybean yield, it is perhaps even more of a concern for its ability to interfere with soybean harvest and reduce soybean seed quality (Milliman et al. 2000). The berries of this plant are capable of staining corn and soybean seeds and the foliage which often remains green at harvest can plug combines and also act as a source of moisture for fungal growth during storage (Ward and Weaver 1996.).

Figure 3: Eastern Black Nightshade plant

Eastern black nightshade is not as commonly encountered as a problematic weed of corn as in soybean, as almost all of our current preplant and post-emergence corn herbicides provide good control of this species. However, the growth habit of eastern black nightshade is well adapted to some of the most common weed management practices utilized in current soybean production systems. For example, eastern black nightshade can germinate after post-emergence applications of glyphosate have been made and these plants are also very shade tolerant in nature. Another common practice once used to control eastern black nightshade was the use of ALS herbicides like the imidazolinones (Pursuit, Scepter, etc.) (Milliman et al. 2000). However, over-use of these herbicides has resulted in the selection for ALS-resistant biotypes of eastern black nightshade in several Midwestern states (Milliman et al. 2000).

One of the best options for the control of eastern black nightshade in soybeans is the application of a preplant, residual herbicide. Most of the currently-labeled preplant herbicides with residual activity provide good to excellent control of eastern black nightshade in soybeans. Previous research has shown that the chloroacetamide herbicides provide good control of this species (Ashigh and Tardif 2006). For this reason, preplant applications of products that contain metolachlor (Dual II Magnum, Prefix, Boundary, etc.), dimethenamid (Outlook, Verdict, etc.) or alachlor (IntRRo, etc.) should be considered in fields where eastern black nightshade is a concern. Additionally, the flumioxazin- and sulfentrazone-based products like Valor, Valor XLT, Envive, Authority Assist, Authority XL, Authority First, Sonic, etc. also provide good control of this species. Lastly, if there are no concerns with ALS resistance in the population, ALS-inhibiting herbicides like Pursuit, Pursuit Plus, and Scepter can still provide good control of this species. As with almost all weeds encountered in soybean systems, narrower soybean row spacings have also been shown to contribute to the overall level of eastern black nightshade control observed. Stoller and Myers (1989) found that switching from 30-inch to 7.5-inch row spacings decreased the growth and fruit production of eastern black nightshade by 50%.